Cardiac pacemakers and other such implantable medical devices (e.g., cochlear implants, defibrillators, neurostimulators, active drug pumps, etc.) typically comprise a hermetically sealed container and a feedthrough assembly having one or more terminals (e.g., niobium pins) that provide conductive paths from the interior of the device to one or more lead wires exterior to the device. In general, such feedthrough assemblies comprise a ferrule that is fixedly coupled (e.g., welded) to a container and an insulating structure disposed within the ferrule. The insulating structure may include joint-insulator sub-assemblies, each of which is disposed around a different terminal pin. For example, the insulating structure may include one or more braze joints, each of which comprises an insulator ring (e.g., glass, ceramic, etc.) that insulates the pin from the ferrule, a pin-insulator braze (e.g., gold) that couples the insulating ring to the pin, and an insulator-ferrule braze (e.g., gold) that couples the insulating ring to the ferrule. When the medical device is implanted, the braze joints may be exposed to body fluids. It is thus important that each of the braze joints forms a hermetic seal between the ferrule and its respective terminal pin. To ensure that a satisfactory seal has been formed, a gas may be introduced through an aperture provided through a wall of the ferrule proximate the braze joint or joints. The aperture is then plugged, and the feedthrough assembly is externally monitored for the gas by way of, for example, a mass spectrometer.
To reduce the effects of stray electromagnetic interference (EMI) signals that may be collected by lead wires coupled to the feedthrough terminal pins, it is known to attach a discoidal capacitor to the feedthrough assembly that permits passage of relatively low frequency electrical signals along the terminal pin or pins while shunting undesired high frequency interference signals to the device's container. Typically, the attachment of such a capacitor includes the thermal curing of one or more non-conductive epoxy preforms to physically couple the capacitor to the insulating structure of the feedthrough.
Although feedthrough filter capacitor assemblies of the type described above perform satisfactorily, the installation of such filter capacitor assemblies poses certain problems related to the curing of the epoxy preforms. For example, the epoxy preforms may wick into the annular cavities provided between the capacitor and the terminal pins during curing and thus occupy space that should be filled by a conductive material (e.g., epoxy, solder, etc.). This results in a degraded electrical connection between the terminal pins and the capacitors. Additionally, the non-conductive epoxy preforms may seep into the insulating structure and cover cracks that have formed through the braze joint. This may prevent gas from being detected during leak testing and, therefore, may create the impression that a satisfactory hermetic seal has been formed when, in fact, one has not.
Considering the above, it should be appreciated that it would be desirable to provide a filtered feedthrough assembly utilizing an improved capacitor attachment technique that prevents the undesired travel of non-conductive epoxy. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.